The correlation of one or more noisy analogue signals may be effective even when the signal is polluted by noise that is of greater amplitude than the signal. One known approach is to correlate the noisy analogue signal with another signal, such as a reference signal of known characteristics. This is achieved by multiplying together the two signals and then integrating the result. When the integral is near-zero, the signals are not correlated. When the integral is strongly positive, the signals are correlated and when the integral is strongly negative, the signals are correlated, but one is inverted in relation to the other.
However, analogue integrators are prone to drift. Furthermore, the multiplication and integration of the two signals is quite resource intensive.
The present invention has been devised in part to address these issues.